Simplify VideoDecodeEngine interface by making everything synchronous.

media/filters/video_renderer_base.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // VideoRendererBase creates its own thread for the sole purpose of timing frame
 // presentation.  It handles reading from the decoder and stores the results in
 // a queue of decoded frames, calling OnFrameAvailable() on subclasses to notify
 // when a frame is ready to display.
 //
 // The media filter methods Initialize(), Stop(), SetPlaybackRate() and Seek()
@@ skipping 70 matching lines @@
   //
   // Implementors should avoid doing any sort of heavy work in this method and
   // instead post a task to a common/worker thread to handle rendering.  Slowing
   // down the video thread may result in losing synchronization with audio.
   //
   // IMPORTANT: This method is called on the video renderer thread, which is
   // different from the thread OnInitialize(), OnStop(), and the rest of the
   // class executes on.
   virtual void OnFrameAvailable() = 0;
 
-  void ReadInput(scoped_refptr<VideoFrame> frame);
+ private:
+  // Callback from the video decoder delivering decoded video frames.
+  void FrameReady(scoped_refptr<VideoFrame> frame);
 
- private:
-  // Callback from video decoder to deliver decoded video frames and decrements
-  // |pending_reads_|.
-  void ConsumeVideoFrame(scoped_refptr<VideoFrame> frame);
+  // Helper method that schedules an asynchronous read from the decoder as long
+  // as there isn't a pending read and we have capacity.
+  void AttemptRead_Locked();
 
-  // Helper method that schedules an asynchronous read from the decoder and
-  // increments |pending_reads_|.
-  //
-  // Safe to call from any thread.
-  void ScheduleRead_Locked();
-
-  // Helper function to finished "flush" operation
-  void OnFlushDone_Locked();
-
-  // Helper method that flushes all video frame in "ready queue" including
-  // current frame into "done queue".
-  void FlushBuffers_Locked();
+  // Attempts to complete flushing and transition into the flushed state.
+  void AttemptFlush_Locked();
 
   // Calculates the duration to sleep for based on |current_frame_|'s timestamp,
   // the next frame timestamp (may be NULL), and the provided playback rate.
   //
   // We don't use |playback_rate_| to avoid locking.
   base::TimeDelta CalculateSleepDuration(VideoFrame* next_frame,
                                          float playback_rate);
 
   // Safely handles entering to an error state.
   void EnterErrorState_Locked(PipelineStatus status);
 
   // Helper function that flushes the buffers when a Stop() or error occurs.
-  void DoStopOrErrorFlush_Locked();
+  void DoStopOrError_Locked();
 
   // Used for accessing data members.
   base::Lock lock_;
 
   scoped_refptr<VideoDecoder> decoder_;
 
   // Queue of incoming frames as well as the current frame since the last time
   // OnFrameAvailable() was called.
-  typedef std::deque< scoped_refptr<VideoFrame> > VideoFrameQueue;
+  typedef std::deque<scoped_refptr<VideoFrame> > VideoFrameQueue;
   VideoFrameQueue frames_queue_ready_;
-  VideoFrameQueue frames_queue_done_;
+
+  // The current frame available to subclasses for rendering via
+  // GetCurrentFrame().  |current_frame_| can only be altered when
+  // |pending_paint_| is false.
   scoped_refptr<VideoFrame> current_frame_;
+
+  // The previous |current_frame_| and is returned via GetCurrentFrame() in the
+  // situation where all frames were deallocated (i.e., during a flush).
+  //
+  // TODO(scherkus): remove this after getting rid of Get/PutCurrentFrame() in
+  // favour of passing ownership of the current frame to the renderer via
+  // callback.
   scoped_refptr<VideoFrame> last_available_frame_;
 
   // Used to signal |thread_| as frames are added to |frames_|.  Rule of thumb:
   // always check |state_| to see if it was set to STOPPED after waking up!
   base::ConditionVariable frame_available_;
 
   // State transition Diagram of this class:
   //       [kUninitialized] -------> [kError]
   //              |
   //              | Initialize()
@@ skipping 30 matching lines @@
     kError,
   };
   State state_;
 
   // Video thread handle.
   base::PlatformThreadHandle thread_;
 
   // Previous time returned from the pipeline.
   base::TimeDelta previous_time_;
 
-  // Keeps track of our pending buffers. We *must* have no pending reads
-  // before executing the flush callback; We decrement it each time we receive
-  // a buffer and increment it each time we send a buffer out. therefore if
-  // decoder provides buffer, |pending_reads_| is always non-positive and if
-  // renderer provides buffer, |pending_reads_| is always non-negative.
-  int pending_reads_;
+  // Keep track of various pending operations:
+  //   - |pending_read_| is true when there's an active video decoding request.
+  //   - |pending_paint_| is true when |current_frame_| is currently being
+  //     accessed by the subclass.
+  //   - |pending_paint_with_last_available_| is true when
+  //     |last_available_frame_| is currently being accessed by the subclass.
+  //
+  // Flushing cannot complete until both |pending_read_| and |pending_paint_|
+  // are false.
+  bool pending_read_;
   bool pending_paint_;
   bool pending_paint_with_last_available_;
 
   float playback_rate_;
 
   // Filter callbacks.
   base::Closure flush_callback_;
   FilterStatusCB seek_cb_;
   StatisticsCallback statistics_callback_;
 
   base::TimeDelta seek_timestamp_;
 
+  VideoDecoder::ReadCB read_cb_;
+
   DISALLOW_COPY_AND_ASSIGN(VideoRendererBase);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_VIDEO_RENDERER_BASE_H_